This invention relates to a floor construction method and system, and more particularly to a method for producing shallow and ultra shallow steel floor systems. Ultra-shallow steel floor systems may be defined as those having depths in the range 100 mm to 350 mm.
In multi-storey buildings it has become increasingly important to minimise the overall floor-to-floor height, and consequently the depth taken up by any floor structure needs to be minimised. This need is driven by increased levels of servicing accommodated within modern ceiling and floor zones, and the desire to accommodate as many floors as possible, without contravening planning restrictions on the allowable overall building height. Historically, very compact construction was achieved by using thin structural concrete slab with closely spaced columns.
In recent years engineers have sought methods to construct equally compact floors in steel rather than concrete. This invention is such a form of construction, being shallower, more practical, more economical and more flexible than existing technology, with the added benefit of achieving larger spans.
In traditional, non-shallow, multi-storey steel construction, a steel I or H-beam spans horizontally between supports, with concrete flooring placed on top of the steel beam spanning between adjacent beams. Thus the steel forms the building skeleton and the horizontal concrete forms the floor. In shallow construction instead of the concrete sitting on top of the steel I or H-beam, it is accommodated within the depth of the beam itself, thus significantly reducing the thickness of the overall floor.
For shallow floor construction it is very difficult to use standard H-section because the concrete flooring unit cannot be safely lowered into place without fouling the projection of the top flange of the H-section.
It is therefore preferable to use an asymmetric steel beam, where the top flange is substantially narrower than the bottom flange. The difference between the two flange widths has to be sufficient to allow the concrete unit to be easily and safely lowered onto the wider bottom flange. Several forms of asymmetric shallow steel beams are known, but each has significant drawbacks.
SLIMDEK ASB® beams are asymmetric steel beams, rolled by Corus. The top flange is 110 mm narrower than the bottom flange. However, these beams have several drawbacks:    a) There is a very limited range of section sizes, consisting of 10 depths in increments between 272 mm to 342 mm;    b) The shallowest, 272 mm deep, is too deep for many ultra-shallow floors;    c) In order to achieve composite action sufficient cover of concrete and reinforcement must be placed over the Slimdek top flange, further increasing depth;    d) Due to the small number of beams in the range, the weight increase from one to the next strongest is very substantial, making for unnecessarily heavy construction.
SLIMFLOR® Beams are standard rolled H-beams with a wide plate welded to the underside of the bottom flange to produce an asymmetric profile. This has the benefit of providing a greater range of beam depths, but is still restricted by the limited range of H-beams available in any market.
Welded Plate Beams can be produced by welding together two horizontal plates separated by a vertical plate to form an I or H-beam. An asymmetric profile is achieved by using horizontal plates of differing widths. The benefit of this is that the depth of the H-beam is totally flexible, as the vertical web-plate can be made to any required depth. However, most commercially available automated welding systems cannot gain access to weld a beam less than 300 mm in depth. Moreover, unless the welds that join the vertical and horizontal plates are full strength butt welds, which are prohibitively expensive, a plate H-beam is significantly inferior to rolled section in its load carrying capacity.
Each of the above types of steel beam have another important practical drawback. In modern buildings, numerous services (such as power cables, communication lines, water pipes, air ducts) are required for each floor of the building. It is advantageous to locate such service structures within the floor construction itself.